1. Field of the Invention
The present invention relates to a spin-valve type thin film magnetic element in which electrical resistance changes in relation to the direction of pinned magnetization of a pinned magnetic layer and the direction of magnetization of a free magnetic layer susceptible to external magnetic fields, and a thin film magnetic head comprising the spin-valve type thin film magnetic element.
2. Description of the Related Art
Magnetoresistive magnetic heads are categorized as an AMR (Anisotropic Magnetoresistive) head comprising an element that exhibits a magnetoresistive effect and a GMR (Giant Magnetoresistive) head comprising an element that exhibits a giant magnetoresistive effect. The Element that exhibits the magnetoresistive effect in the AMR head comprises a monolayer structure made of a magnetic material. The element in the GMR head comprises, on the other hand, a multilayer structure of a plurality of laminated materials. Among several structures that yield the giant magnetoresistive effect, a spin-valve type thin film magnetic element has a relatively simple structure and high rate of change of resistivity against weak external magnetic fields.
FIG. 9 shows a cross section of one example of the structure of the conventional spin-valve type thin film magnetic element viewed from the opposite face side to a recording medium.
Shield layers are formed on and under the spin-valve type thin film magnetic element 30 in this example separated by gap layers (insulation layers), and a regenerative GMR head is composed of the spin-valve type thin film magnetic element 30, gap layers and shield layers. A recording inductive head may be laminated on the regenerative GMR head.
This GMR head as well as the inductive head are provided at the end of the trailing side of a floating type slider to sense the recorded magnetic field of a magnetic recording medium such as a hard disk.
In FIG. 9, the magnetic recording medium travels in the Z direction in the drawing, and the leakage magnetic field from the magnetic recording medium is directed in the Y-axis in the drawing.
The spin-valve type thin film magnetic element 30 shown in FIG. 9 is a so-called bottom type single spin-valve type thin film magnetic element in which one layer each of an antiferromagnetic layer, a pinned magnetic layer, a non-magnetic conductive layer and a free magnetic layer are formed.
In FIG. 9, the reference numeral 33 denotes a lower shield layer with a lower gap layer (an insulation layer) 31 formed on this lower shield layer 33, and an antiferromagnetic layer 22 is formed on the gap layer 31. In addition, a pinned magnetic layer 23 is formed on the antiferromagnetic layer 22, a non-magnetic conductive layer 24 made of, for example, Cu is formed on the pinned magnetic layer 23, and a free magnetic layer 25 is formed on the non-magnetic conductive layer 24.
A pair of bias layers 26, 26 are laminated on the free magnetic layer 25 separated by a pair of ferromagnetic layers 27, 27 made of, for example, a NiFe alloy with a distance apart in the X1 direction in the drawing. A pair of conductive layers 28, 28 made of, for example, Cu are further provided on the bias layers 26, 26.
A gap layer 32 covering the conductive layers 28, 28 and free magnetic layer 25 and made of Al2O3 is additionally laminated on the conductive layers.
A shield layer (an upper shield layer) 34 is laminated on the gap layer (the upper gap layer) 32.
The antiferromagnetic layer 22 made of an antiferromagnetic material such as a FeMn alloy is laminated to be in contact with the pinned magnetic layer 23 so that an exchange coupling magnetic field (an exchange anisotropic magnetic field) is generated at the interface between the pinned magnetic layer 23 and antiferromagnetic layer 22 to fix the magnetization direction of the pinned magnetic layer 23 in the Y direction in the drawing, or in the direction departing from the recording medium (the height direction).
The pinned magnetic layer 23 is made of, for example, a Co film, a NiFe alloy, CoNiFe alloy or CoFe alloy.
The bias layers 26, 26 made of an antiferromagnetic material such as an IrMn alloy are laminated in contact with the antiferromagnetic layers 27, 27, and generate an exchange coupling magnetic field (an exchange anisotropic magnetic field) at the interface between the bias layers 26 and antiferromagnetic layers 27. The magnetization direction of the free magnetic layer 25 is aligned in the direction opposed to the X1 direction in the drawing by this exchange coupling magnetic field to suppress Barkhausen noises by putting the free magnetic layer 25 into a single magnetic domain state, thereby allowing the magnetization direction of the free magnetic layer 26 to be approximately perpendicular to the magnetization direction of the pinned magnetic layer 23.
Since a pair of the bias layers 26 and 26 are laminated with a distance apart with each other, a portion that is not laminated with the bias layer 26 remains on the free magnetic layer 25, and this portion serves as a track portion G2 of the thin film magnetic head.
The magnetization direction of the free magnetic layer shifts from the direction opposed to the X1 direction to the Y direction in this spin-valve type thin film magnetic element 30, when a steady-state current flows from the conductive layer 28 to the free magnetic layer 25, non-magnetic conductive layer 24 and pinned magnetic layer 23, and when a leakage magnetic field is applied in the Y direction from the magnetic recording medium traveling in the Z direction. The electric resistance changes in relation to the change of the magnetization direction in the free magnetic layer 25 and the magnetization direction of the pinned magnetic layer 23, and the leakage magnetic field from the magnetic recording medium is sensed by voltage changes based on the resistance changes.
The spin-valve type thin film magnetic element 30 shown in FIG. 9 functions so as to align the magnetization direction of the free magnetic layer 25 so that it comes in substantially perpendicular the magnetization direction of the pinned magnetic layer 23 by an exchange bias method using the bias layer 26 made of an antiferromagnetic material.
The bias layers 26 and the antiferromagnetic layer 22 are formed using an antiferromagnetic material such as an InMn alloy that is susceptible to heat in the spin-valve type thin film magnetic element 30 shown in FIG. 9. Accordingly, the exchange coupling magnetic field (Hex) generated at the interface between the bias layer 26 and antiferromagnetic layer 27 decreases by a heat treatment at 200° C. or more in the manufacturing process of the spin-valve type thin film magnetic element, or by the heat generated by the steady-sate sensing current when the element is used as a magnetic head. Consequently, the pinning magnetic field of the exchange bias for aligning the magnetization direction of the free magnetic layer 26 in the direction opposed to the X1 direction is weakened, and magnetic domains of the free magnetic layer 25 are hardly controlled or the pinning magnetic field becomes unstable.
Since the bias layer 26 in the vicinity of the track portion 26a is thinned when the bias layers 26 and conductive layers 28 are formed by a so-called lift-off method, the exchange coupling magnetic field generated at the interface between the track portion 26a of the track layer 26 and the ferromagnetic layer 27 is decreased. The magnetization direction at the portion 27a in the vicinity of the ferromagnetic layers 27 is disturbed and fails in aligning in the direction opposed to the X1 direction. Consequently, the magnetization direction at the portion 25a at both sides of the track portion of the free magnetic layer 25 is not aligned in the opposed direction to the X1 direction, thereby generating an abnormal output waveform at both ends of the track width Tw.
The bias layer 26 should be as thick as about 50 nm in order to certainly align the magnetization direction of the free magnetic layer 25. In addition, since the conductive layers 28 are required to have some thickness in order to allow a sensing current to flow, a large step height 32a is formed in the vicinity of the track portion of the gap layer 32. Consequently, the shape of the writing magnetic gap of the recording inductive head laminated on the spin-valve type thin film magnetic element is distorted and the magnetic recording pattern recorded on the magnetic recording medium becomes irregular, possibly causing an error during regeneration. When the bias layers 26 and the conductive layers 28 are thick, on the other hand, the distance L1 between these bias layers 26 and the conductive layers 28, and the upper shield layer 34 is shortened to make it difficult to securely insulate the shield layer 34 from the spin-valve type thin film magnetic element 3.